linux-kernel - Re: [PATCH v2 1/3] tty: Add functions for handling flow control chars

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Message-ID: <YlAuUpOZ4IVqZTFk@smile.fi.intel.com>
Date:   Fri, 8 Apr 2022 15:45:06 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial <linux-serial@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v2 1/3] tty: Add functions for handling flow control chars

On Fri, Apr 08, 2022 at 03:20:07PM +0300, Ilpo Järvinen wrote:
> On Fri, 8 Apr 2022, Andy Shevchenko wrote:
> > On Fri, Apr 08, 2022 at 02:39:52PM +0300, Ilpo Järvinen wrote:
> > > Move receive path flow control character handling to own function
> > > and a helper.
> > > 
> > > This seems cleanest approach especially once skipping due to lookahead
> > > is added. Its downside is the duplicated START_CHAR and STOP_CHAR
> > > checks.
> > > 
> > > No functional changes.
> > 
> > But it seems the change. See below.
> > 
> > ...
> > 
> > > +static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
> > > +{
> > > +	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
> > > +}
> > > +
> > > +/* Returns true if c is consumed as flow-control character */
> > > +static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
> > > +{
> > > +	if (!n_tty_is_char_flow_ctrl(tty, c))
> > > +		return false;
> > > +
> > > +	if (c == START_CHAR(tty)) {
> > > +		start_tty(tty);
> > > +		process_echoes(tty);
> > 
> > > +	} else if (c == STOP_CHAR(tty)) {
> > 
> > In the original code no 'else' was present.
> >
> > Perhaps it's not a functional change, but this detail has to be explained.
> 
> Correct that the previous code didn't have else, however, there was return 
> with the same effect. Adding this else here was no accident from my part 
> but it is intentionally there to have no functional change for the 
> START_CHAR == STOP_CHAR case!

Perhaps you can split this change to a separate patch with this explanation
given.

> > > +		stop_tty(tty);
> > > +	}
> > > +
> > > +	return true;
> > > +}


-- 
With Best Regards,
Andy Shevchenko